Many integrated circuits include a buried N layer that serves to electrically isolate electronic components produced over the buried N layer. A buried N layer is doped with “N” conductivity-determining ions and overlies a substrate lightly doped with “P” conductivity-determining ions, and a monocrystalline layer overlies the buried N layer. A well tap extends through the monocrystalline layer and the buried N layer, and the substrate under the buried N layer is biased or electrically charged to prevent noise or charge migration induced by high voltage electronic components on the monocrystalline layer. The electric charge is induced into the substrate through the well tap. The buried N layer is often used with bipolar transistor devices, or integrated circuits using both bipolar and complementary metal oxide semiconductor (CMOS) transistors, but the buried N layer can be beneficial in other uses as well.
Existing methods for fabricating a buried N layer produce a “step” or raised surface of the substrate. The step height is normally in the range of about 500 to about 1,000 angstroms, and this step is transferred to the monocrystalline layer when it is formed overlying the substrate. The step is used to aid in mask alignment, but the step remains in the monocrystalline layer that overlies the buried N layer. Before manufacturing electronic components, the monocrystalline layer is leveled by chemical mechanical planarization to provide a smooth, flat surface. The uneven surface with “steps” complicates leveling by chemical mechanical planarization, and the leveling process becomes more difficult with smaller integrated circuits. The varying surface height also interferes with photoresist patterning because the depth of focus changes with the uneven surface height.
Accordingly, it is desirable to provide integrated circuits with buried N layers where the monocrystalline layer upper surface is smooth and flat. In addition, it is desirable to provide methods for producing such integrated circuits with fewer manufacturing steps to help control production costs. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.